Pulp screening machine



Se t. 25, 1934. A. J. HAUG 1,974,651

PULP SCREENING MACHINE Filed March 17, 19253 5 Sheets-Sheet 1 1 7i .2 a .9 b

INVENTOR,

'- ATTORNEY? Sept. 25, 1934. A. J. H UG 1,974,651

PULP SCREENING MACHINE Filed March 17, 1933 3 Sheets-Sheet 2 MNVENTZRI 4 1 ATTORNEY.

Sept, 25, 1934. J AUG 1,974,651

PULP SCREENING MACHINE Filed March 17, 1933 3 Sheets-Sheet 3 I Patented Sept. 25,- 1934 UNITED STATES PATENT OFFICE 17 Claims.

This invention relates to machines for screening paper making stock or pulp. As is well understood by those skilled in the art of paper making, the pulp or stock from which the paper is made is delivered to the paper making wire in a relatively dilute condition, usually containing in the neighborhood of .4% or .5% of solid constituents. Before the stock flows to the wire it passes through a pulp screening machine which removes the slivers, coarse particles, matted fibers, and the like, allowing only the fine stock to go through to the paper making operation. In addition to this final screening operation the pulp usually is subjected to similar operations at preceding points in the preparation of the stock.

The present invention relates to machines of this character and is more especially concerned with that type of pulp screening machine in which the stock flows inwardly from the outer to the inner side of the screening drum. A typical machine of this type includes a screening drum, usually of substantially cylindrical form, mounted in a casing having suitable inlet and outlet connections. The stock or pulp to be screened is delivered to the interior of the casing at a point outside of the drum, flows through the screening surface of the drum, and is discharged from the casing. The coarser materials or tailings which cannot pass through the screen accumulate on its .outer surface and mechanism of some kind usually is provided to remove these coarser constituents from said surface. The proper handling of these coarser materials or tailings presents a difficult problem because of their tendency to cling to the surface of the screen notwithstanding the action of the scrapers or other devices provided to remove them. Their presence on the screen, however, interferes seriously with the screening operation since they tend to felt on to the screen or to form a mat which not only impedes the screening action but substantially reduces the capacity of the machine.

The present invention is especially concerned with the handling of the tailings in a machine of the inflow type. It aims to deal with this problem more effectively and to improve the efliciency of pulp screening machines of the inflow type with a view to increasing their screening capacity without substantially increasing their power consumption.

The nature of the invention will be readily understood from the following description when read in connectionwith the accompanying drawings, and the novel features will be particu arly pointed out in the appended claims.

so controlled as to maintain this condition. The

In the drawings,

Figure 1 is a vertical, longitudinal, sectional view of a pulp screening machine constructed in accordance with this invention;

Fig. 2 is a transverse, sectional view on the line 2-2, Fig. 1;

Fig. 3 is a view similar to Fig. 1 showing another embodiment of the invention;

Fig. 4 is a sectional view on the line 44, Fig. 3;

Fig. 5 is a view similar to Fig. 1 showing still another form which the invention may take;

Fig. 6 is a transverse, vertical, sectional viewof the machine shown in Fig. 5.

Referring first to Figs. 1 and 2, the machine there shown comprises a casing 2 supported on a suitable base 3. Mounted in the casing is a stationary screening drum 4 provided with a closed end 5. In this particular arrangement the drum is supported entirely at its left-hand end, the casing being provided with a circular flanged member 6 which is bolted to the end plate of the casing and on which the drum is rigidly secured. The stock to be screened is conducted into the easingthrough an inlet spout 7, the stock usually being fed to the machine from a headbox (not shown) of a common type, so that the pulp flows into the machine under a definite and fixed head. This pulp substantially fills the space in the easing around the screen 4, its rate of delivery being greater part of it flows through the apertures in the screening surface, but the screen rejects the slivers and coarser materials which cannot pass through the slots or perforations in the drum. Usually a head of screened stock is maintained inside the screen by means of a weir 8 which closes the lower part of the outlet opening 10 in the easing, the height of the weir being made such as to maintain any desired head of screened stock in the drum. The stock overflowing the weir is conducted to the thickening machine, the paper making wire, or to the next machine which is to operate on it.

It will be observed that in this machine the entire outer surface of the screen is maintained constantly submerged .in unscreened stock while approximately the lower half of the inner surface is constantly submerged in screened pulp or fine stock. The stock usually flows much more rapidly through the lower half of the screen than through the upper part due to the fact that since both surfaces of the lower part of the screen are submerged, a better suspension of the fibre as it comes to the screen is maintained in the lower screening areas.

As above stated, the coarser constituents of the stock which are rejected by the screen tend to accumulate on the outer surface of the screen and to build up a mat which reduces the screening capacity of the machine and impedes the screening operation. For the purpose of obviating this difficulty a series of arms 12 are mounted to revolve around the screen closely adjacent to its outer surface. All of these arms are secured in and supported by an upright disk 13 located immediately behind, or at the right, Fig. 1, of the closed end 5 of the screening drum, the arms projecting horizontally from the margin of this disk. A shaft 14 integral with, or secured to, the disk 13, and mounted in suitable bearings, supports the disk 13 in its operative position, the shaft carrying a pulley 15 by means of which it may be belted to any convenient source of power.

When the machine is in operation the arms 12 revolve around the screen 4 closely adjacent to it and tend to carrya considerable volume of the unscreened pulp circumferentially around the screen. The rate of rotation of the arms usually need not be sufficient to set up a high degree of centrifugal force in the unscreened pulp slnce such a force will oppose the hydraulic head maintained on the pulp in the casing and thus increase the head or external force required to produce the necessary flow of stock through the screen. The arms must, however, produce a rotary motion of the stock around the circumference of the screen sufficient for the purposes hereinafter described.

Mounted in the casing around the screen are several deflectors 16, preferably secured rigidly to the casing and so positioned as to act on the rotating body of unscreened stock to deflect said stock and to produce areas of increased pressure each followed by an area of reduced pressure. Considering for the moment the uppermost deflector 16 shown in Fig. 2, it will be evident that as the body of stock revolving with the arms 12 moves past the lower curved surface of the deflector, this surface will tend to increase the pressure serving to force the stock inwardly through the screen. Such pressure reaches a maximum at the edge a, Fig. 2. Immediately beyond, or at the right of this point, the deflector is cut away sharply so that as soon as the stock has passed this edge the inward pressure is relieved and an eddy is formed which, because of the motion of the stock past the cutaway edge, produces a reverse or outward flow of fluid through the screening surface. Such an outward movement exerts a strong tendency to lift the tailings away from the screening surface, and this action takes place through a strip of the screening surface extending the entire length of the deflector. The same action occurs at each of the other deflectors, and any suitable number of them may be used to suit the requirements of individual machines.

Certain of the arms 12, as for example, those indicated at b, are made in the form of scrapers and are located somewhat closer to the screen than are the other arms so that they will strike the tailings loosened by the outward movements of the stock. In addition, these arms b are inclined, as indicated in Fig. 1, in such a direction as to cause their contact with the tailings to force the tailings along the screening surface toward the left-hand end, Fig. 1, of the drum. These arms act on the tailings at a time when the latter are in a free or floating condition, and when, consequently, relatively little force is required to move the tailings in the desired direction. The heavier constituents of the tailings settle to the bottom of the casing and may be drawn off through the pipe or conduit 17 equipped with a valve 18. The lighter constituents are forced into a discharge pipe 20 leading from the upper part of the casing and are conducted to some suitable point of discharge.

Such an arrangement, therefore, substantially improves the screening conditions in the machine and results in a corresponding improvement in efficiency. In the machine shown in Figs. 1 and 2 the areas through which the outward flow occurs consist of longitudinally extending strips of the screening surface located closely adjacent to the cutaway ends of the deflectors. A further improvement in screening efliciency can therefore be obtained by relatively rotating the deflectors and the screen to effect a relative transfer of these areas around the entire screening surface and thus to maintain approximately the entire screening area substantially free from undesirable accumulations of coarse materials. Such a result can be accomplished either by revolving the screen, as in the arrangement shown in Figs. 3 and 4, or by rotating the casing, as in the construction illustrated in Figs. 5 and 6.

In the machine shown in Figs. 3 and 4, the casing 2 with its deflector 16, inlet 7 and its tailings outlets 17 and 20 are arranged approximately as in the construction shown in Figs. 1 and 2. This machine also includes a screen 4 and arms 12 mounted to revolve around it. In this machine, however, the screening drum comprises two end members 21 and 22, both supported for rotation, and the latter member is secured in the end of a hollow shaft 14 carrying a pulley 15'. Consequently, by belting this pulley to a suitable source of power the screen 4 may be revolved at any desired speed.

In this machine also the arms 12 are carried by an end member or disk 13 which is secured fast on a sleeve or bushing 23 in which the drum shaft 14 revolves, the bushing, in turn, being mounted to rotate in a bearing carried by one of the end members of the machine caring. For the purposeof rotating the sleeve 23 and the arms 12, a back gearing connection is provided between the sleeve and the shaft 14'. Such connection includes a gear 24, fast on the shaft 14, and driving a pinion 25 secured on one end of a shaft 26, this shaft carrying a similar pinion 27 on its opposite end which meshes with and drives a gear 28 fast on the sleeve 23. Usually the gear ratio is made such that the screen revolves rather slowly and the arms 12 rotate at a somewhat higher speed and in the same direction as the screen.

This machine may be operated in the same general manner as that above described, the pulp being delivered to it in essentially the same way, this pulp flowing through the screen into the interior thereof in approximately the manner above described in connection with Figs. 1 and 2. An outflow of the stock at localized areas extending longitudinally of the screen is produced by the rotation of the unscreened stock around the drum and the reaction of this stock with the deflectors 16. Due to the fact, however, that the screen is constantly moving through the areas of outward flow, the entire surface of the screen, other conditions being equal, is maintained in a better screening condition than in the construction previously described. In this machine, also, the tailings are forced toward one end of the screen and are removed in the manner explained above.

A different arrangement may be provided for delivering the screened stock. That shown consists of a stationary receiver 30 located inside the screen and having an open end projecting through the left-hand end, Fig. 3, of the casing. The opposite end of the receiver is partly closed and is provided with a stub shaft 31 which projects into a bore in the end member 22 of the screen and serves as .a' support for the inner end of the receiver. The upper side of the receiver is left open and a scraper 32 is extended diagonally upward from the rearward edge of the opening in it and to a point closely adjacent to the inner surface of the screen, as shown in Fig. 4, where it will catch the screened stock carried around by the motion of the drum. This stock flows into the receiver and out through the open end. The end of the scraper may be made adjustable, as shown, to control the depth of stock held on the inside of the screen.

In the machine shown in Figs. 5 and 6, the screen 4 is supported in the casing in the same manner as in the construction shown in Figs. 1 and 2 and the arms 12 are similarly supported and driven. The central section 2 of the casing, however, is mounted to revolve around an axis substantially coinciding with that of the screen cylinder 4, the end sections of the casing being provided with suitable bearing surfaces to support the central section 2' for this movement. Secured fast on one end of the section 2' is a gear ring 34 meshing with a pinion 35 fast on a shaft 36 which is driven by a belt connection with the shaft 14. In this particular construction, also, the deflectors or pulsators are formed integral with the casing, the parts 37 of the casing section 2' cor esponding to the deflectors 16 and performing essentially the same function as that served by said deflectors.

In operation this machine performs in much k the same manner as that shown in Figs. 1 and 2.

An important difference, however, is the fact that the deflectors or pulsators 37 are constantly revolving at a slow speed around the stationary screen 4 and thus transfer the areas through which an outflow of stock isv maintained serving to loosen the tailings. Certain of the arms 12 are inclined, as in the constructions above described, and thus serve to force the tailings toward the left-hand end of the casing. Preferably the casing is tapered, as shown in Fig. 5, with its larger end located at the left-hand end of the screen. Also, an annular enlargement 38 of the casing is provided at the larger end of the rotating section 2' of the casing, serving to collect.

.similar to that shown in my prior Patent No. 1,882,662 for controlling the discharge of the materials rejected by the screen.

Fig. '7 shows a structural variation of the easing illustrated in Figs. 5 and 6 without the screening drum or the rotating arms.

In all three of the machines illustrated the screening conditions are greatly improved and the efficiency of the machine is increased by the use of the arrangements above described forloosening the tailings and moving them along the screen toward one end thereof.

While I have herein shown and described tyD cal embodiments of my invention, it will be evident that the invention may be embodied in other forms without departing from the spirit or scope thereof. For example, the casing may be made in various shapes and some of the features of the invention may be utilized in vertical screens as well as in those of the horizontal type. The arms also may take different forms while still performing essentially the same functions. For example, the rotary motion of the stock along the peripheral surface of the drum and circumferentially thereof could be produced by a foraminous drum located in a position corresponding to that occupied by the arms and having relatively large holes through it so .that it would act on the stock in essentially the same manner as do the arms while still permitting the reverse impulses to be transmitted through it. In fact, a drum made of heavy wire screening might be used to produce this effect. For most purposes, however, I prefer to use a construction more like those shown in the drawings.

Having thus described/my invention, what I desire to claim as new is:

1. In a pulp screening machine, the combination of a screening drum, a casing in which said drum is mounted, an inlet for conducting stock to be screened into said casing at a point outside of said drum where it will flow inwardly through the screening surface of the drum into the interior thereof, means located closely adjacent to said screening surface for rotation around the axis of the drum to move the stock adjacent to said drum along said screening surface circumferentially thereof, driving mechanism for revolving said means, and means for acting on the stock so set in motion to change its direction and then by to produce temporary localized reversals of the normal flow of stock through said screening surface.

2. In a pulp screening machine, the combination of a screening drum, a casing in which said drum is mounted, an inlet for conducting stock to be screened into said casing at a point outside of said drum where it wi l -flow inwardly through the screening surface ofthe drum into the interior thereof, means located closely adjacent to said screening surface for rotation around theaxis of the drum to move the stock adjacent to said drum along said screening surface circumferentially thereof, driving mechanism for revolving said means, and additional means for causing the motion of the stock so produced to create temporary localized reversals of the normal flow of stock through said screening surface to loosen the'tailing's which cling to said surface.

3. In a pulp screening machine, the combination of a screening drum, a casing in which said drum is mounted, an inlet for conducting stock to be screened into said casing at a point outside of said drum where it will flow inwardly through the screening surface of the drum into the interior thereof, means located closely adjacent to said screening surface for rotation around the axis of the drum to move the stock. adjacent to said drum along said screening surface circumferentially thereof, driving mechanism for revolving said means, and a deflector for acting on the body of stock so set in motion to cause said movement of the stock to produce a.

temporary outward flow of stock through a strip of the screening surface extending longitudinally thereof.

4. A machine according to preceding claim 3 including means for relatively revolving said defiector and said drum to transfer the area in which said reversal is produced around the screening surface of the drum.

' 5. A machine according to preceding claim 2 including mechanism for relatively rotating said screen and said additional means.

6. A machine according to preceding claim 2 including mechanism for rotating said.- drum around its own axis.

7. A machine according to preceding claim 2 including mechanism for revolving said casing around said drum.

8. In a pulp screening machine, the combination of a screening drum, a casing in which said drum is mounted, an inlet for conducting stock to be screened into said casing at a point outside of said drum where it will flow inwardly through the screening surface of the drum into the interior thereof, means for supporting a plurality of arms closely adjacent to said screening surface for rotary motion around the axis of the drum, driving mechanism for revolving said arms around said axis to cause them to move the stock adjacent to said drum along said screening surface circumferentially thereof, means for maintaining a head of screened stock within said drum, and means for causing the motion of the stock circumferentially of said screening surface to create temporary localized movements of said stock outwardly through said screening surface.

9. In a pulp screening machine, the combination of a screening drum, a casing in which said drum is mounted, an inlet for conducting stock to be screened into said casing at a point outside of said drum where it will flow inwardly through the screening surface of the drum into the interior thereof, means for acting on the stock to produce a temporary localized outward flow of the stock through the screening surface to loosen the tailings that cling to said surface, means for acting on the tailings so loosened to move them along said screening surface toward one end of said drum, and means for conducting the tailings out of said casing.

10. In a pulp screening machine, the combination of a screening drum, a casing in which said drum is mounted, an inlet for conducting stock to be screened into said casing at a point outside of said drum where it will flow inwardly through the screening surface of the drum into the interior thereof, means for acting on the stock to produce a temporary localized outward flow of the stock through the screening surface to loosen the tailings that cling to said surface, means for acting on the tailings so loosened to move them along said screening surface toward one end of said drum, and a tailings outlet leading from said casing at a point below said drum at one end thereof.

11. In a pulp screening machine, the combination of a screening drum, a casing in which said drum is mounted, an inlet for conducting stock to be screened into said casing at a point outside of said drum where it will flow inwardly through the screening surface of the drum into the interior thereof, means for acting on the stock to produce a temporary localized outward flow of the stock through the screening surface to loosen the tailings that cling to said surface, means for acting on the tailings so loosened to move them along said screening surface toward one end of said drum, and mechanism for relatively rotating said screen and said first mentioned means to transfer the point at which said outward flow occurs circumferentially around the screen, said casing having a recess for collecting and holding said tailings in a region partly protected from the motion of the stock.

12. In a pulp screening machine, the combination of a screening drum, a casing in which said drum is mounted, an inlet for conducting stock to be screened into said casing at a point outside of said drum where it will flow inwardly through the screening surface of the drum into the interior thereof, means for acting on the stock to produce a temporary localized outward flow of the stock through the screening surface to loosen the tailings that cling to said surface, means for acting on the tailings so loosened to move them along said screening surface toward one end of said drum, said casing being tapered and having its larger end located adjacent to the end of the drum to which the tailings are moved, and means for conducting the tailings away from the latter end of said drum and out of the casing.

13. In a pulp screening machine, the combination of a screening drum, a casing in which said drum is mounted, an inlet connection for conducting stock to be screened into said casing and outside of said drum where it will flow inwardly through the screening surface of said drum into the interior thereof, means for supporting a plurality of arms closely adjacent to said screening surface for rotary motion around the periphery of the drum, driving mechanism for revolving said arms around said drum to cause them to create a rotary motion in the unscreened stock closely adjacent to the screening surface of the drum, and additional means for causing the stock so set in motion to produce temporary localized reversals of the normal inflow of stock through said screening surface.

14. In a pulp screening machine, the combination of a screening drum, a casing in which said drum is mounted, an inlet connection for conducting stock to be screened into said casing and outside of said drum where it will flow inwardly through the screening surface of said drum into the interior thereof, means for supporting a plurality of arms closely adjacent to said screening surface for rotary motion around the periphery of the drum, driving mechanism for revolving said arms around said drum to cause them to create a rotary motion in the unscreened stock closely adjacent to the screening surface of the drum, and means for revolving said drum in the same direction as said arms but at a different speed from that of the arms.

15. In a pulp screening machine, the combination of a screening drum, a casing in which said drum is mounted, an inlet for conducting stock to be screened into said casing at a point outside of said drum where it will flow inwardly through the screening surface of the drum into the interior thereof, means for acting on the stock to produce a temporary localized outward flow of the stock through the screening surface to loosen the tailings that cling to said surface, means for acting on the tailings so loosened to move them along said screening surface toward one end of said drum, mechanism for relatively rotating said screen and said first mentioned means to transfer the point at which said outward flow occurs circumferentially around the screen, and means operable substantially continuously for withdrawing the tailings from said casing.

16. In a pulp screening machine, the combinadrum to relatively move said arms along said screening surface circumferentially thereof, and 'means for causing the motion of the stock circumferentiallyof said screening surface to create localized movements of said stock outwardly through said screening surface and thereby to loosen the tailings that cling to said surface, one

or more of said arms being inclined to act on the tailings so loosened to move them along said screening surface toward one end of said drum.

17. In a pulp screening machine, the combination of a screening drum, a casing in which said drum is mounted, an inlet for conducting stock to be screened into said casing at a point outside of said drum where it will flow inwardly through the screening surface of the drum into the interior thereof, means for acting on the stock to produce a temporary localized outward flow of the stock through the screening surface to loosen the tailings that cling to said surface, and means for acting on the tailings so loosened to move them along said screening surface toward one end of said drum.

ANTON JOSEPH HAUG. 

